Optical techniques cannot be used to observe extremely fine features such as those on the surface of a semiconductor integrated circuit, because the wavelength of visible light is too large to distinguish such fine features. Therefore, particles in the form of an electron beam are used because an electron beam can be generated with a sufficiently small wavelength to distinguish such features.
Three types of electron beam microscopes have been developed: Transmission Electron Microscope (TEM), Scanning Transmission Electron Microscope (STEM), and Scanning Electron Microscope (SEM). Each of these microscopes operates by accelerating an electron beam toward the surface of an object to be viewed. To prevent an electric charge from accumulating on the surface, the object is often coated with a metal before being bombarded with an electron beam. When an electron beam strikes the surface of the object, secondary electrons are emitted from the object. The secondary electrons are collected by a detector, known as a secondary emission detector (SED). The detected secondary emission is then coordinated with the excitation signals applied to the electron beam to extract an image of the object.
The TEM, which is very expensive, generates an unmovable electron beam spot through a thin object of interest to produce an image of very high resolution. The STEM, which is also very expensive, generates an electron beam that is scanned through a thin object of interest to produce an image of very high resolution. The SEM, which is approximately ten times less expensive than either a TEM or a STEM, generates an electron beam that is scanned over a solid object of interest to produce an image of high resolution, but not as high as either a TEM or a STEM.
U.S. Pat. No. 4,596,929 entitled “THREE-STAGE SECONDARY EMISSION ELECTRON DETECTION IN ELECTRON MICROSCOPES,” discloses a device that uses two grids to maximize the amount of secondary emission detected by a detector. The present invention does not employ two such grids. U.S. Pat. No. 4,596,929 is hereby incorporated by reference into the specification of the present invention.
U.S. Pat. No. 4,627,009 entitled “MICROSCOPE STAGE ASSEMBLY AND CONTROL SYSTEM,” discloses a device for rotating and tilting a sample in a non-eucentric manner and compensate for the same so that an inspection point is within the field of view. The present invention does not rotate and tilt a sample in a non-eucentric manner and compensate for the same so that an inspection point is within the field of view. U.S. Pat. No. 4,627,009 is hereby incorporated by reference into the specification of the present invention.
U.S. Pat. No. 4,950,909 entitled “SAMPLE TILTING DEVICE IN ELECTRON MICROSCOPE,” discloses a device for tilting a sample wherein no change in the field of view occurs when the sample is rotated conically about an axis. The present invention does not tilt and rotate a sample so that no change in the field of view occurs. U.S. Pat. No. 4,950,909 is hereby incorporated by reference into the specification of the present invention. U.S. Pat. No. 5,179,280, entitled “COMPUTER CONTROL OF THE ELECTRON MICROSCOPE SAMPLE STAGE,” discloses a device for tilting a sample so that a plurality of different orientations are displayed stereoscopically with a spot representing a current orientation. The present invention does not tilt a sample so that a plurality of different orientations are displayed stereoscopically with a spot representing a current orientation. U.S. Pat. No. 5,179,280 is hereby incorporated by reference into the specification of the present invention.
U.S. Pat. No. 5,510,624, entitled “SIMULTANEOUS SPECIMEN AND STAGE CLEANING DEVICE FOR ANALYTICAL ELECTRON MICROSCOPE,” discloses a device for cleaning a sample stage, a sample, and an interior of an analytical electron microscope. The present invention does not clean a sample stage, a sample, and an interior of an analytical electron microscope. U.S. Pat. No. 5,510,624 is hereby incorporated by reference into the specification of the present invention.
U.S. Pat. No. 6,025,592, entitled “HIGH TEMPERATURE SPECIMEN STAGE AND DETECTOR FOR AN ENVIRONMENTAL SCANNING ELECTRON MICROSCOPE,” discloses a device that can heat a sample to 1500 degrees Celsius. The present invention does not heat a sample to 1500 degrees Celsius. U.S. Pat. No. 6,025,592 is hereby incorporated by reference into the specification of the present invention.
U.S. Pat. No. 6,407,850, entitled “AUTO TILT STAGE,” discloses a device for tilting a sample stage of a TEM microscope to multiple positions. The present invention does not tilt a sample stage of a TEM microscope to multiple positions. U.S. Pat. No. 6,407,850 is hereby incorporated by reference into the specification of the present invention.
U.S. Pat. No. 6,777,678, entitled “SAMPLE-STAGE FOR SCANNING ELECTRON MICROSCOPE,” discloses a device for measuring a sample with a SEM. A collimator and reflector are used to increase the image resolution of a horizontal sample imaged with a SEM to that of the STEM. The present invention does not image a horizontal image. U.S. Pat. No. 6,777,678 is hereby incorporated by reference into the specification of the present invention.
There exists a need to increase the resolution of images from a SEM without incurring the expense of either a STEM or a TEM, and without incurring the expense and inconvenience of creating a thin sample.